1. Field
This invention relates to the art of providing visual traffic marking devices for paved aircraft landing and takeoff strips and automobile roadways Still more particularly, the invention concerns the utilization of retroreflective and fluorescent materials and the like to provide nighttime visibility at safe distances from oncoming aircraft and ground vehicles.
2. State of the Art
Currently, the predominant material for traffic lane marking is light colored paint applied directly to the traffic surface. It is economical to apply, but is so rapidly eroded by traffic and weather that it must be replaced with costly frequency. It also suffers from inadequate visibility even at moderate distances. The patent literature describes several possibly more durable and visible traffic marking devices. U.S. Pat. No. 3,011,412 discloses a method of embedding beads or other autocollimating units into a viscous, self-hardening resin based paint. The paint is applied upstanding from the traffic surface, as a center line strip, for example, and then covered with an erodeable or water soluble layer for temporary protection from traffic during the setting period. A pyramidal roadway reflector is disclosed in U.S. Pat. No. 3,627,403, designed to extend upwardly from a roadway surface. The sloping side faces of the pyramid incorporate reflective prisms covered by a transparent plastic layer. In U.S. Pat. No. 4,279,471 an elongate transparent base member is installed extending upwardly from a roadway surface. A reflective element is inserted into a lengthwise channel in the base member. All of these reflective devices protrude upwardly, obstructing and interrupting the smooth traffic surface, and constituting traffic hazards. Further, snow plows and other cleaning machines tend to damage such upstanding devices. In an attempt to alleviate this problem, U.S. Pat. No. 4,685,824 discloses a traffic marking device embedded with its upper surface even with the traffic surface. However, the only reflectivity provided is by surface beads or the like. No vertical profile is provided, so that its visibility is greatly reduced at moderate distances from the lights of the oncoming vehicles. Thus, the prior art reflective marking devices commonly either protrude upwardly from the traffic surface or suffer seriously decreased visibility from moderate distances. The latter shortcoming is particularly serious for airport landing and takeoff strips, often requiring visibility from up to a mile or more. The prior art also falls short in providing for guiding markers operative without reliance upon vehicle lights. With malfunctioning inoperative lights, the aircraft must at present hope for a not always available illuminated landing strip. Even with functioning lights, the pilot must know the strip location well enough to position his craft to direct light upon reflective markers. No practical, economical method of independently illuminating the marker is found in the prior art. Clearly, there is a need for a traffic marking device with long distance nighttime visibility, which does not interrupt the traffic surface, and is not rapidly eroded to require frequent maintenance and replacement. A further need is for such a marker with provisions for independent, nighttime self-illumination.